Hi Mark,
Terminology is not just pedantry, it's important for good communication, and good communication is important for getting issues resolved.
"Import" is the process by which Aperture gets to know about your images. Before import it doesn't know your images exist. After import, it does. But this doesn't say anything about whether those images are Managed or Referenced. Whether an image is managed or referenced is down to how you imported them and the settings you specified for that import.
Here are the various badges and what they mean:
No badge means the file is managed and the image is available
This badge means the file is referenced and the image is available (online)
This badge means the file is referenced and the image is not available (the referenced drive is not online)
This badge means the image is not available, but the drive where the image should be located is online. Unfortunately it doesn't help you distinguish between managed ot referenced, the same badge is used for both, so it could be either.
Data loss is very rare, but when it does occur it is more often because the concept of manged versus referenced has not been understood. For example, a user will import into Aperture but (perhaps accidentally, or unkowingly) specify the files remain in their original location (making them referenced). Thinking the files have been copied into Aperture, the user deletes the images (or re-purposes the drive where they were located), and the images are now lost.
Like I say, this is rare but it would be useful to know (for sure) if your images were managed or referenced and unfortunately just telling me they were imported in Aperture doesn't tell me this.
In your case, I really don't think your images are lost. I think it is much more likely that your issue is due to the way the library has been moved to different types of advanced storage. If the images were referenced, the fix is simple (use 'Locate referenced files' and please note, this is a different option to 'Relocate Originals') but if they were managed it's a little more complicated and involves looking into your library with finder (or Maybe Terminal), so it would be useful to know what the actual situation is before proceeding.
For example, can you remember which, if any, of these badges the images had when you first imported them?
Andy
Edited for spelling grammer (why isn't spell checking available in this edit window?)